Composition optimization of TC21 titanium alloy based on cluster-plus-glue-atom model
The composition of high-damage-tolerance dual-phase TC21 (Ti-6Al-2Zr-2Sn-2Mo-2Nb-1.5Cr) were analyzed on the basis of the dual-cluster formula of Ti-6Al-4V,consisting of 13 α-Ti and 4 β-Ti unit.Its β-Ti unit is reduced from 5 to 4 compared with Ti-6Al-4V,while adding more β-stabilizing elements to enhance the strength and plasticity.Subsequently,the atoms of each β-stabilizing element within the β-Ti cluster formula of TC21 were proportioned equally to increase the mixing entropy,and more Zr content was increased to substantially enhance the β-phase stability,giving the cluster formula as α-{[Al-Ti12](AlTi2)}13+β-{[(Al-(Ti12Zr2)]Sn0.75Mo0.75Nb0.75Cr0.75}4(atom fraction),named as TC21Z2,with the corresponding mass fraction of Ti-5.9Al-5.4Zr-2.6Sn-2.1Mo-2.0Nb-1.1Cr.The samples were prepared by using vacuum copper mold pouring process and the as-cast microstructure and tensile mechanical properties of the alloy were studied.Results show that the as-cast microstructure of TC21Z2 is composed of α+α' martensite+a small amount of β phases,and its ultimate tensile strength,yield strength and elongation are 1289,1181 MPa and 1.4％,respectively.Its strength and plasticity are better than those of the TC21 at the same state.
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